很简单
原式=1+3+5+7+9+11+1/2*3+1/3*4+1/4*5+1/5*6+1/6*7
=12+12+12+1/2-1/3+1/3-1/4+1/5-1/6+1/6-1/7
=36+1/2-1/7
=36又5/14